This invention generally concerns the art of phosphate conversion coating treatments that are executed on the surfaces of such metals as iron, steel, zinc-plated steel sheet, aluminum, and magnesium alloys. More specifically, the invention concerns a composition and process for conditioning metal surfaces prior to such conversion treatments in order to accelerate the conversion reactions, shorten the treatment time, and microsize the phosphate coating crystals.
The formation of dense, microfine phosphate coating crystals is considered desirable both within the realm of automotive phosphate treatments and within the realm of the phosphate treatments associated with plastic working. The formation of such a coating is considered desirable in the former case in order to improve the post-painting corrosion resistance and in the latter case in order to reduce friction during pressing and extend the life of the press tool. In order to obtain dense, microfine phosphate coating crystals, a surface conditioning process is executed prior to the phosphate conversion coating treatment, with a goal of activating the metal surface and producing nuclei for deposition of the phosphate coating crystals. The following treatment sequence is a generalized example of the phosphate conversion coating processes used to produce dense, microfine phosphate coating crystals:
(1) Degreasing;
(2) Tap water rinse (multistage);
(3) Surface conditioning;
(4) Phosphate conversion coating treatment;
(5) Tap water rinse (multistage);
(6) Purified water rinse.
The surface conditioning step is used to induce the formation of dense, microfine phosphate coating crystals. Compositions used for this purpose are known from, for example, U.S. Pat. Nos. 2,874,081, 2,322,349, and 2,310,239, in which titanium, pyrophosphate ions, orthophosphate ions, and sodium ions are disclosed as the main constituent components in the surface conditioning agent. These surface conditioning compositions, known as jernstedt salts, contain titanium ions and titanium colloid in aqueous solution.
The titanium colloid becomes adsorbed on the metal surface when the degreased, water-rinsed metal is dipped in or sprayed with an aqueous solution of the surface conditioning composition. The adsorbed titanium colloid forms nuclei for deposition of the phosphate coating crystals in the ensuing phosphate conversion coating treatment and thereby supports and induces an acceleration of the conversion reactions and a microfine-sizing and densification of the phosphate coating crystals. The surface conditioning compositions currently in commercial use all employ Jernstedt salts, but a number of problems have been associated with the use in surface conditioning processes of titanium colloids obtained from Jernstedt salts.
A first problem is the timewise deterioration in the surface conditioning liquid composition. Aqueous solutions that have just been prepared from the prior-art surface conditioning compositions are in fact very effective in terms of microfine-sizing and densification of the phosphate coating crystals. However, within several days after preparation of the aqueous solution, these baths suffer from a loss of activity due to aggregation of the titanium colloidxe2x80x94regardless of whether or not the surface conditioning liquid composition has been used during this period of time. This loss of activity results in a coarsening of the phosphate coating crystals.
In order to deal with this problem, Japanese Laid Open (Kokai or Unexamined) Patent Application Number Sho 63-76883 (76,883/1988) has disclosed a method for maintaining and managing the surface conditioning activity. In this method, the average particle size of the titanium colloid in the surface conditioning liquid composition is measured and the surface conditioning liquid composition is continuously discharged so as to maintain the average particle size below a specific constant value. In addition, surface conditioning composition is supplied in an amount sufficient to compensate for the amount discharged. While this method does make possible a quantitative management of the primary factor related to the activity of the surface conditioning liquid composition, it also requires the discharge of surface conditioning liquid composition in order to maintain the activity. Moreover, this method requires the discharge of large amounts of surface conditioning liquid composition in order to maintain the same liquid composition activity as in the initial period after preparation of the aqueous solution. This creates issues with regard to the waste water treatment capacity of plants that employ this method, and as a result the activity is actually maintained through a combination of continuous discharge of the surface conditioning liquid composition and total renewal.
A second problem is that the activity and life of the surface conditioning liquid composition depend strongly on the quality of the water used for surface conditioning liquid composition build up. Industrial water is typically used to build up surface conditioning baths. However, as is well known, most industrial water contains cationic components, e.g., calcium and magnesium, that make the water xe2x80x9chardxe2x80x9d, and the content of this component varies as a function of the source of the industrial water. It is known that the titanium colloid which is the main component of the prior-art surface conditioning baths carries an anionic charge in aqueous solution and is maintained in a nonsedimenting, dispersed state by the corresponding electrical repulsive forces. When the cationic component in industrial water is present in a large amount, the titanium colloid is electrically neutralized by the cationic component, so that the electrical repulsive forces are no longer effective and the activity of the titanium colloid is thereby nullified due to the occurrence of aggregation and sedimentation.
The addition of condensed phosphates such as pyrophosphates to surface conditioning baths has been proposed in order to sequester the cationic component and thereby maintain the stability of the titanium colloid. However, when added in large amounts to a surface conditioning liquid composition, the condensed phosphate reacts with the surface of the steel sheet to form a coating, which results in the production of conversion defects in the ensuing phosphate conversion coating treatment. Finally, in localities that suffer from very high magnesium and calcium concentrations, the surface conditioning liquid composition must be built up and supplied with water using pure water, which is very uneconomical.
A third problem involves the temperature and pH conditions that must be used during the surface conditioning process. Specifically, surface conditioning activity cannot be generated at a temperature in excess of 35xc2x0 C. and a pH outside 8.0 to 9.5 due to aggregation of the titanium colloid. This has necessitated the use of very specific temperatures and pH ranges when using the prior-art surface conditioning compositions. This has also made it impossible to achieve cleaning and activation of metal surfaces on a long-term basis using a single liquid composition formulated by the addition of surface conditioning composition to a degreaser.
A fourth problem is the lower limit on the microfine-sizing of the phosphate coating crystals that can be obtained through the activity of the surface conditioning liquid composition. The surface conditioning activity is obtained by the adsorption of the titanium colloid on the metal surface to form nuclei for deposition of the phosphate coating crystals. Thus, finer, denser phosphate coating crystals will be obtained as larger numbers of colloidal titanium particles become adsorbed on the metal surface during the surface conditioning process.
From this one might at first draw the conclusion that the number of titanium colloid particles in the surface conditioning liquid composition should simply be increased, i.e., that the concentration of the titanium colloid should be raised. However, when this concentration is increased, the frequency of collisions among the colloidal titanium particles in the surface conditioning liquid composition is also increased, and these collisions cause aggregation and precipitation of the titanium colloid. At present the upper limit on the usable titanium colloid concentration is xe2x89xa6100 parts per million by weight, hereinafter usually abbreviated as xe2x80x9cppmxe2x80x9d, and it has been impossible in the prior art to obtain additional microfine-sizing of phosphate coating crystals simply by increasing the titanium colloid concentration beyond this level.
These problems have resulted in the appearance of methods that use surface conditioning agents other than Jernstedt salts. For example, Japanese Laid Open (Kokai or Unexamined) Patent Application Numbers Sho 5-156778 (156,778/1981) and Sho 57-23066 (23,066/1982) disclose surface conditioning methods in which the surface of steel strip is pressure-sprayed with a suspension containing the insoluble phosphate salt of a divalent or trivalent metal. However, since these methods manifest their effects only when the suspension is pressure-sprayed against the workpiece, they often cannot be used for surface conditioning in existing phosphate conversion coating treatment plants where this surface conditioning is carried out by ordinary dipping or spraying.
Japanese Published Patent Application (Kokoku or Examined) Number Sho 40-1095 (1,095/1965) has disclosed a surface conditioning method in which zinc-plated steel sheet is immersed in a very concentrated suspension of the insoluble phosphate salt of a divalent or trivalent metal. The working examples provided for this method are limited to zinc-plated steel sheet and have to use very high concentrations of insoluble phosphate salt of at least 30 grams per liter, hereinafter usually abbreviated as xe2x80x9cg/Lxe2x80x9d, at a minimum in order to obtain surface conditioning activity.
In sum, then, notwithstanding the various problems associated with Jernstedt salts and the various tactics that have been proposed for dealing with these problems, up to now there has yet to appear a technology capable of replacing the use of Jernstedt salts in practical phosphating operations.
The present invention seeks to solve at least one of the problems described hereinabove for the prior art and takes as its object the introduction of a novel, highly time-stable surface conditioning liquid composition and process that can be used to achieve at least one of an acceleration of the conversion reactions, a shortening of the treatment time in phosphate conversion coating treatments, and inducement of microfine-sized phosphate coating crystals.
The inventors discovered that solid divalent or trivalent metal phosphate powder of a particular size and concentration (i) will adsorb onto the surface of a metal workpiece in an aqueous solution that contains a particular accelerant component to form nuclei for the ensuing deposition of phosphate coating crystals and (ii) will provide additional improvements in the reaction rate of the phosphate conversion treatment. The major compositional invention accordingly is a surface conditioning liquid composition that characteristically contains at least one phosphate powder selected from phosphates that contain at least one divalent and/or trivalent metal and are sufficiently low in water solubility to remain in the solid state when dispersed as a fine powder in the surface conditioning liquid composition and also contains as accelerant component at least one selection from the group consisting of the following subgroups:
(1) monosaccharides, polysaccharides, and derivatives thereof;
(2) orthophosphoric acid, condensed phosphoric acids, and organophosphonic acid compounds;
(3) water-soluble polymers that are homopolymers or copolymers of vinyl acetate and derivatives of these homopolymers and copolymers;
(4) copolymers and polymers as afforded by the polymerization of:
(a) at least one selection from:
monomers, exclusive of vinyl acetate, that conform to general chemical formula (I): 
xe2x80x83where R1=H or CH3 and R2=H, C1 to C5 alkyl, or C1 to C5 hydroxyalkyl; and
other xcex1,xcex2-unsaturated carboxylic acid monomers; and, optionally,
(b) not more than 50% by weight of monomers that are not vinyl acetate and are not within the description of part (a) immediately above but are copolymerzable with said monomers that are within the description of said part (a).
The total accelerant component selected from immediately previously recited subgroups (1) to (4) preferably has a concentration from 1 to 2,000 ppm in said surface conditioning liquid composition.
The aforesaid phosphate powder preferably includes particles with sizes no greater than 5 micrometers, hereinafter usually abbreviated as xe2x80x9cxcexcmxe2x80x9d, and independently is preferably present at a concentration from 0.001 to 30 g/L, more preferably at least, with increasing preference in the order given, 0.01, 0.10, 0.30, 0.50, 0.70, 0.90, or 0.99 g/L. Moreover and independently, the divalent and/or trivalent metal present therein is preferably at least one selection from Zn, Fe, Mn, Ni, Co, Ca, and Al.
In a preferred embodiment said surface conditioning liquid composition also contains alkali metal salt, ammonium salt, or a mixture of alkali metal salt and ammonium salt. This alkali metal salt or ammonium salt is preferably at least one selection from orthophosphate salts, metaphosphate salts, orthosilicate salts, metasilicate salts, carbonate salts, bicarbonate salts, nitrate salts, nitrite salts, sulfate salts, borate salts, and organic acid salts and independently is preferably present at a concentration of 0.5 to 20 g/L.
A process according to the present invention for conditioning metal surfaces prior to the phosphate conversion coating treatment thereof characteristically comprises effecting contact between the metal surface and a surface conditioning liquid composition according to the invention as described above.
The surface conditioning liquid composition according to the present invention has a much better high-pH stability and high-temperature stability than the colloidal titanium of the prior art and as a consequence, through the addition to this liquid composition of alkali builder plus nonionic or anionic surfactant or mixture thereof, can also be used in a process for simultaneously executing degreasing and surface conditioning in which the metal surface is both cleaned and activated.
An example is provided below of the separate operations of a phosphate conversion coating treatment in which the surface conditioning liquid composition according to the present invention is used for degreasing and surface conditioning in a single process operation:
(1) degreasing and surface conditioning in a single process operation;
(2) phosphate conversion coating treatment;
(3) tap water rinse (multistage); and
(4) pure water rinse.
The use of the surface conditioning liquid composition according to the present invention to effect degreasing and surface conditioning in a single process operation makes possible omission of the water rinse step between degreasing and surface conditioningxe2x80x94a feature heretofore unavailable in the prior art. Moreover, since the surface conditioning liquid composition according to the present invention can be used over a broad pH range and can tolerate the addition of various alkali metal salts, the degreasing and surface conditioning in a single process operation that is identified as process operation (1) above can be preceded by a preliminary cleaning or a preliminary degreasing depending on the particular surface contamination status of the metal workpiece.
The essential components in the present invention are the accelerant component and the metal phosphate powder selected from phosphates that contain at least one divalent and/or trivalent metal (hereinafter usually abbreviated simply as the xe2x80x9cphosphate powderxe2x80x9d). This phosphate powder, being a component that is the same as or similar to that in phosphate conversion baths and phosphate conversion coatings, will not negatively affect the phosphate conversion liquid composition even when carried over thereinto. Another advantage to this phosphate powder is that it also does not negatively affect the performance of the phosphate conversion coating even when taken into the phosphate conversion coating through formation of the nuclei in the phosphate conversion coating. The following can be provided as examples of the phosphate powder used by the present invention: Zn3(PO4)2, Zn2Fe(PO4)2, Zn2Ni(PO4)2, Ni3(PO4)2, Zn2Mn(PO4)2, Mn3(PO4)2, Mn2Fe(PO4)2, Ca3(PO4)2, Zn2Ca(PO4)2, FePO4, AlPO4, CoPO4, Co3(PO4)2, sufficiently water insoluble hydrates of all of these phosphate salts.
The particle size of the phosphate powder used in the present invention is preferably not more than, with increasing preference in the order given, 5.0, 4.0, 3.5, 3.0, 2.5, 20, or 1.7 xcexcm in order to also induce a stable dispersion of the insoluble material in the aqueous solution. At the same time, however, the presence in the surface conditioning liquid composition of the present invention of additional phosphate powder with particle sizes greater than 5 xcexcm has no adverse influence whatever on the advantageous effects of the present invention, which will appear once the concentration of xe2x89xa65 xcexcm microparticles in the surface conditioning liquid composition reaches a certain concentration.
The desired particle size, and possibly other desirable characteristics, of the solid phosphate power used in a composition according to the invention, are readily and therefore preferably obtained by grinding, most preferably ball milling, a suspension of the solid phosphate in water in which an accelerant component as defined above is dissolved until the desired particle size is achieved. If a ball mill is used, the balls are preferably of a very hard ceramic, most preferably zirconia, and independently preferably have a diameter that is not more than, with increasing preference in the order given, 5, 3, 2.0, 1.5, 1.0, 0.80, 0.70, 0.60, or 0.50 millimeters.
Not only does the phosphate powder used in the present invention form nuclei for deposition of the phosphate crystals, this powder also functions to accelerate the deposition reactions. The concentration of the phosphate powder is preferably from 0.001 to 30 g/L in order to form nuclei for phosphate crystal deposition and accelerate the initial phosphate crystal deposition reactions. A phosphate powder concentration less than 0.001 g/L (i) can not satisfactorily accelerate the initial phosphate crystal deposition reactions, because of the correspondingly small amount of phosphate powder adsorbed on the metal surface and (ii) also will not satisfactorily accelerate the reactions due to the correspondingly small number of divalent or trivalent metal phosphate particles functioning as nuclei. A phosphate powder concentration in excess of 30 g/L is simply uneconomical, because no additional acceleration of the phosphate conversion reactions is obtained at concentrations above 30 g/L.
The present inventors discovered that surface conditioning activity appears in the presence of any of the accelerant components of the present invention as described herein, even when treatment is carried out by dipping at low concentrations of the phosphate powder and without the application of any physical force to the metal surface that is greater than the force supplied by conventional process operations, such as dipping, stirring, spraying, pumping, or the like that are conventionally used with prior art titanium colloidal activators, The present invention operates simply through contact between the workpiece and the surface conditioning liquid composition and thus operates on a reaction mechanism that is entirely different from that of the prior art that requires robust physical force to accelerate solid phosphate salt particles into the surface being conditioned.
The concentration of the accelerant component in the composition is preferably from 1 to 2,000 ppm. At concentrations below 1 ppm a satisfactory surface conditioning activity usually can not be produced by simple contact between the metal workpiece and the surface conditioning liquid composition. Not only can no additional effects be expected at concentrations in excess of 2,000 ppm, but such concentrations may result in an excessive adsorption by the accelerant component on the surface of the metal workpiece and hence hinder the phosphate conversion activity.
The basic structural unit saccharide of the monosaccharides, polysaccharides, and derivatives thereof used as accelerants in the present invention can be selected from, for example, fructose, tagatose, psioose, sofbose, erythrose, threose, ribose, arabinose, xylose, lyxose, allose, altrose, glucose, mannose, gulose, idose, galactose, and talose. (For the purposes of the present invention, a substance that produces two or more saccharide units by hydrolysis of each molecule is designated as a polysaccharide and a saccharide that itself can not be hydrolyzed further to produce a lower molecular weight saccharide is designated as a monsaccharide.)
In the case of the monosaccharides, the basic structural saccharides described above will be used as such; in the case of the polysaccharides, homolysaccharides or heteropolysaccharides of the aforementioned basic structural saccharides can be used; finally, derivatives of the preceding can be afforded by the substitution of the hydrogen atom of at least one of the hydroxyls in the basic saccharide by a substituent moiety such as xe2x80x94NO2, xe2x80x94CH3, xe2x80x94C2H4OH, xe2x80x94CH2CH(OH)CH3, and xe2x80x94CH2COOH. Combinations of several species of monosaccharides, polysaccharides, and derivatives thereof can also be used.
The advantageous effects of the invention are independent of the configuration and optical rotation of the basic structural saccharide and the invention can therefore use any combination of D-monosaccharides and L-monosaccharides and both dextrorotatory and levorotatory optical rotations. Nor will any problem be created by the use of the sodium or ammonium salt of the aforementioned monosaccharides, polysaccharides, and derivatives thereof in order to improve the water solubility of same. Moreover, when the preceding structures are poorly soluble in water, they can be used after preliminary dissolution in an organic solvent that is miscible with water.
Examples of suitable accelerant component substances from the above-described subgroup (2) are: pyrophosphoric acid, tripolyphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid, hexametaphosphodc acid, aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic add, and the sodium and ammonium salts of the preceding, and the sodium and ammonium salts of any of the preceding acids in this sentence. The invention can use a single selection or any combination thereof.
Subgroup (3) of suitable accelerant components as described above are exemplified by polyvinyl alcohols afforded by the hydrolysis of vinyl acetate polymers, cyanoethylated polyvinyl alcohols afforded by the cyanoethylation of such polyvinyl alcohols with acrylonitrile, formalated polyvinyl alcohols afforded by the acetalation of such polyvinyl alcohols with formaldehyde, urethanized polyvinyl alcohols afforded by the urethanation of such polyvinyl. alcohols with urea, and water-soluble polymer compounds afforded by the introduction of the carboxyl group, sulfonic group, or amide group into polyvinyl alcohol. Monomers copolymerized with vinyl acetate can be exemplified by acrylic add, crotonic acid, and maleic anhydride. The beneficial effects associated with the present invention will be fully manifested as long as the vinyl acetate polymers or derivatives thereof and/or the copolymers of vinyl acetate and monomers copolymerizable therewith are sufficiently soluble in water. As a result, these effects are independent of the degree of polymerization and degree of functional group introduction of the subject polymers. The invention can use a single selection from the above-described polymers and copolymers or can use any combination thereof.
In connection with subgroup (4) as defined above of suitable accelerant substances:
monomers that conform to general chemical formula (I) can be exemplified by methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypentyl acrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, and hydroxypentyl methacrylate; The xcex1,xcex2-unsaturated carboxylic acid monomers other than acrylic and methacrylic acids can be exemplified by maleic acid and crotonic acid;
monomers copolymerizable with the preceding monomers can be exemplified by styrene, vinyl chloride, and vinylsulfonic acid;
the invention can use polymer synthesized by the polymerization of a single monomer from among the preceding or copolymer synthesized by the polymerization of any combination of the preceding monomers.
The surface conditioning liquid composition according to the present invention can also contain an alkali metal salt or ammonium salt or a mixture thereof. Suitable alkali metal salts and ammonium salts are exemplified by orthophosphate salts, metaphos phate salts, orthosilicate salts, metasilicate salts, carbonate salts, bicarbonate salts, nitrate salts, nitrite salts, sulfate salts, borate salts, and organic acid salts. The invention can also use combinations of two or more selections from the aforesaid alkali metal and ammonium salts.
The alkali metal and ammonium salts used by the present invention in general will be equivalent to the alkali builders used in commercial cleaning agents. As a consequence, the activities associated with the alkali builders in commercial cleaning agents, i.e., the ability to soften hard water and cleaning activity with respect to oil, will provide activity as a cleaning agent as well as additional improvements in the liquid composition stability of the surface conditioning liquid composition used by the present invention.
The concentration of the alkali metal salt or ammonium salt is desirably from 0.5 to 20 g/L. The hard water softening activity and cleaning activity will not usually be satisfactory at concentrations below 0.5 g/L, while concentrations in excess of 20 g/L are simply uneconomical because no additional benefits are obtained at such concentrations.
Unlike the prior-art technologies, the surface conditioning liquid composition according to the present invention has the ability to retain its effects and activities in almost any use environment. Thus, the present invention provides at least one, and in favorable instances all, of the following advantages over the prior art-technologies:
(1) higher time-wise stability;
(2) less deterioration in conditioning activity when hardness components such as Ca and Mg increase in concentration in the liquid composition;
(3) ability to be used at higher temperatures;
(4) ability to be mixed with various alkali metal salts without substantial reduction in its conditioning activity; and
(5) higher stability over a wider pH range.
The liquid composition according to the present invention can therefore be used to carry out degreasing and surface conditioning in a single process operation, although prior-art technologies have been unable to continuously maintain stable qualities in this type of use. In addition to the above-described alkali metal or ammonium salts, the liquid composition according to the present invention can also tolerate the addition of other known inorganic alkali builders, organic builders, and surfactants for the purpose of improving the cleaning performance in such a degreasing +surface conditioning in a single process operation. Moreover, irrespective of the execution of degreasing and surface conditioning in a single process operation, a known sequestering agent and/or condensed phosphate can be added in order to mitigate any adverse influence of cationic component carried over into the surface conditioning liquid composition.
A surface conditioning process according to the present invention may be carried out simply by effecting contact between the metal surface and a surface conditioning liquid composition according to the invention as described above; such factors as the contact time and temperature of the surface conditioning liquid composition are not usually critical. Furthermore, the surface conditioning process according to the present invention can be applied to any metal on which phosphate treatment is executed, e.g., iron and steel, zino-plated steel sheet, aluminum, aluminum alloys, and magnesium alloys.
The phosphate conversion treatment executed after the surface conditioning treatment according to the present invention can employ any methodology, e.g., dipping, spraying, electrolysis, and the like. The particular phosphate coating deposited is not critical as long as it is a phosphate conversion coating, e.g., a zinc phosphate, manganese phosphate, or calcium/zinc phosphate conversion coating.
The use of a surface conditioning liquid composition according to the present invention will be described in greater detail below through working and comparative examples. The phosphating treatment used in the examples is a zinc phosphating treatment for underpaint applications, but this treatment is provided simply as one example of phosphating treatments and in no way limits the applications of the surface conditioning liquid composition of the present invention.
Substrates
The designations and properties of the sample sheets used as the substrate surface treated In the working and comparative examples were as follows (xe2x80x9cJISxe2x80x9d means xe2x80x9cJapanese Industrial Standardxe2x80x9d and xe2x80x9cg/m2xe2x80x9d means xe2x80x9cgrams per square meterxe2x80x9d):
SPC (cold-rolled steel sheet according to JIS G-3141);
EG (steel sheet electrogalvanized on both surfaces, with zinc add-on weight of 20 g/m2);
GA (steel sheet, hot-dip galvannealed on both surfaces, with zinc add-on weight=45 g/m2);
Znxe2x80x94Ni (steel sheet, Zn/Ni alloy electroplated on both surfaces, plating weight=20 g/m2);
Al (aluminum sheet according to JIS 5052); and
MP (magnesium alloy sheet according to JIS H-4201).
Process Operation Sequence
Each of the sample sheets was treated using the following sequence unless otherwise explicitly noted: alkaline degreasingxe2x86x92water rinsexe2x86x92surface conditioning treatmentxe2x86x92formation of zinc phosphate coatingxe2x86x92water rinsexe2x86x92rinse with deionized water.
In both the working and comparative examples, the alkaline degreasing used a 120 second spray at 42xc2x0 C. of a solution of FINECLEANER(copyright) L4460 concentrate (a commercial product of Nihon Parkerizing Co., Ltd.) that had been diluted with tap water to 2% of the concentrate.
The surface conditioning treatment was run by dipping the workpiece in the particular surface conditioning liquid composition described below in each of the working and comparative examples.
In order to form the zinc phosphate coating, in both the working and comparative examples PALBOND(copyright) L3020 concentrate (a commercial product of Nihon Parkerizing Co., Ltd.) was diluted with tap water to 4.8% and the component concentrations, total acidity, free acidity, and accelerant concentration were adjusted to the concentrations currently in general use for automotive zinc phosphate treatments. The resulting liquid composition was contacted with the substrates by dipping them into the surface conditioning liquid composition for 120 seconds at 42xc2x0 C.
Both the tap water rinse and the pure water rinse used a 30-second spray at room temperature.
Tests for Evaluating the Zinc Phosphate Coatings
The coating appearance (xe2x80x9cCAxe2x80x9d), coating weight (xe2x80x9cCWxe2x80x9d), coating crystal size (xe2x80x9cCSxe2x80x9d), and (only on the SPC substrates) the xe2x80x9cP ratioxe2x80x9d were measured, by the methods described immediately below, on the zinc phosphate coatings formed after the surface conditioning treatment.
Coating appearance (CA): the presence/absence of coating voids and nonuniformity was evaluated visually and was scored on the following scale:
++: uniform. good-quality appearance;
+: nonuniform in some regions, but with no visually apparent voids;
xcex94: presence of some minor voids along with nonuniformity;
xc3x97: substantial area fraction of voids; and
xc3x97xc3x97: no conversion coating present.
Coating weight (CW): The weight of the sample sheet was measured after formation of the zinc phosphate coating to give the value W1 (in grams, hereinafter usually abbreviated as xe2x80x9cgxe2x80x9d). The zinc phosphate coating was then stripped (stripping liquid composition and conditions given below) and the weight was again measured to give W2 (also in g). The coating weight was calculated from the following equation:
coating weight (g/m2)=(W1xe2x88x92W2)/(surface area).
For the cold-rolled steel sheets the stripping liquid was 5% chromic acid (i.e., CrO3) solution in water, and the stripping conditions were 75xc2x0 C., 15 minutes, by dipping. For the galvanized steel sheet the stripping liquid composition was a solution containing 2% by weight of ammonium dichromate, 49% by weight of 28% by weight ammonia solution in water, and 49% by weight of pure water, and the stripping conditions were ambient temperature (i.e., 18-23xc2x0 C.), 15 minutes, by dipping.
For the magnesium alloy and aluminum: The amount of elemental phosphorus in the zinc phosphate coating was quantitated using an X-ray fluorescent analyzer and the add-on weight of the coating was calculated from the P content, assuming that the coating was hopeite.
Coating crystal size (CS): The crystal size was determined by inspection of an image of the zinc phosphate coating obtained using a scanning electron microscope (xe2x80x9cSEMxe2x80x9d) at 1,500 times magnification.
xe2x80x9cP ratioxe2x80x9d: This value was determined by measuring the X-ray intensity of the phosphophyllite crystals (xe2x80x9cPxe2x80x9d) and the X-ray intensity of the hopeite crystals (xe2x80x9chxe2x80x9d) in the zinc phosphate coating, using an x-ray diffraction instrument. The xe2x80x9cP ratioxe2x80x9d was calculated from the following equation, using the thus obtained x-ray intensity values: xe2x80x9cP ratioxe2x80x9d=p/(p+h).
Table 1 reports the compositions of surface conditioning baths provided as examples of Claim one of the present invention, Table 2 reports the compositions of the various surface conditioning baths provided as comparative examples (including some with details explained below). The monosaccharides, polysaccharides, and derivatives thereof used in the working and comparative examples were commercial products obtained from, for example, Daicel Kagaku Kogyo Kabushiki Kaisha, Dai-ichi Kogyo Seiyaku Kabushiki Kaisha, Asahi Kasei Kogyo Kabushiki Kaisha, and Dainippon Seiyaku Kabushiki Kaisha. This component was selected taking into account such factors as the type of basic structural saccharide, degree of polymerization, substituents, and degree of substitution. The substituents are exemplified for the case of glucose, a basic structural sac charide, using the following chemical structure: 
In the case of glucose, the 3 hydroxyls at R1, R2, and R3 can be etherified. In the examples under consideration, the type of substituent and degree of substitution (number of hydroxyl groups that have been substituted by the substituent(s) per unit of the basic structural saccharide) were varied in order to investigate the corresponding effects. The polysaccharide, or derivative thereof. In the ageing test, the surface conditioning liquid composition was allowed to stand for 10 days at room temperature after preparation and was then used.